Carat (or karat, abbreviated to 'ct' or 'K') is a system used to indicate the purity of gold. It is measured as 24 times the purity divided by mass, which means that 24 carat is the purest form (the object will be at least 99% pure gold). 18 carat gold is 18 parts gold, six parts composed of another metal.

Different carat marks are more common in different countries – for example, the gold produced in the UK is commonly 9 – 22 carat, whereas 24 carat is associated with the Middle East, China, Malaysia and Indonesia. 18 carat gold is the standard gold value found in the southern Mediterranean countries such as Italy.

Brussels is the capital city of Belgium and the largest urban settlement in the country, with around 1.1 million inhabitants. It is also the appointed capital of the European Union, housing the headquarters of NATO, UITP and other EU insitutions.

Brussels grew from a chapel on the River Senne which was built around 580 AD; the city was officially found in 979. The name derives from the Old Dutch ‘Broeksel’, meaning ‘home in the marsh’. As part of the Habsburg Empire, Brussels was the capital of the Low Countries until the area was annexed by France in 1795. In 1815 it became part of the Kingdom of the Netherlands, but in 1830 the Belgian revolution took place and Belgium became a separate country with Brussels its capital.

Throughout most of its history Brussels was a Dutch-speaking city with French an administrative language; the city was officially declared bilingual in 1921. During World War Two it was spared major damage despite German occupation, and since the end of the war has been a major convention centre for European politics.

BMW (Bayerische Motoren Werke AG) is a German company manufacturing cars, motorbikes and engines. Founded in 1917 in Bavaria, the company retains its headquarters in the city of Munich.

BMW originally produced aircraft, but after the First World War ended in 1918 it was no longer allowed to make aeroplanes and therefore moved into motor vehicles. Its well-known circular logo combines the blue and white of the Bavarian flag.

BMW produced around 1.5 million vehicles in 2010. As well as BMW cars and motorbikes, it produces Mini cars and Husqvarna bikes, and is the parent company of Rolls-Royce cars.

BMW enjoyed some success in Formula One racing, including with Robert Kunica, but retired from the sport at the end of the 2009 season.

London Bridge spans the River Thames in central London, between Southwark and the City. The first bridge was a timber structure built by the Romans which was replaced and improved several times until the first stone version was completed in 1209.

During medieval times, buildings stood on the bridge, whose ends were marked by Southwark Cathedral and the church of St Magnus the Martyr. The southern entrance to the bridge was the site at which the severed heads of executed traitors were displayed as a warning to the public – one of London’s most infamous sights.

London Bridge today, with the City in the background - Credit: David Williams

The houses on the bridge were demolished in 1758-1762 and the bridge span widened to aid the navigation of the river. ‘New’ London Bridge was built in the early 19th century, and the current structure replaced it in 1973.

London Bridge is one of the city’s icons, regularly shown in films, and has found its way into the annals of popular history in the children’s nursery rhyme ‘London Bridge Is Falling Down’ due to its regular collapses and replacements. At its foot are The London Tombs/The London Bridge Experience, a popular tourist attraction which shows visitors a tour through London’s darker history.

The clock tower of Big Ben at the Palace of Westminster - Credit: David Iliff

The bell in Westminster’s clock tower is known as Big Ben – a name which extends to the clock face – and is a London landmark and British icon. It is the largest four-faced chiming clock in the world and has stood at the north end of the Palace of Westminster since 1859.

Named in honour of Sir Benjamin Hall, the MP and civil engineer responsible for its installation, the 13.5 ton bell has been cracked since 1859 when the striking hammer damaged it – despite this, the bell continues to chime, albeit with a slight twang. Four other bells housed in the belfry play the Westminster Quarters every fifteen minutes.

In June 2012, the bell tower was renamed the Elizabeth Tower in honour of Queen Elizabeth’s Diamond Jubilee. Although not open to the public, it is possible to arrange a tour of the tower to see Big Ben through an MP.